1. Field of the Invention
The invention relates to a structure of a rotary electric machine including a stator and a rotor. More particularly, the invention relates to a structure of a stator.
2. Description of the Related Art
Conventionally, as a stator of a rotary electric machine including a stator and a rotor (e.g., a synchronous motor), a stator of a rotary electric machine has been employed in which a nozzle is inserted into a slot, that is formed between teeth arranged in a stator core, from the inner peripheral side, that is, the side on which there is the axis of rotation of the synchronous motor, and a coil is wound around each of the teeth multiple times (this method is so-called nozzle direct winding). The nozzle direct winding for the stator core provides robustness and is low in cost.
Also, for a stator of a rotary electric machine, a structure is employed in which an electromagnetic member (i.e., a coil) is fitted to the stator having a continuous inner periphery at a portion between teeth and the electromagnetic member is fixed, whereby a proportion of a cross sectional area of the coil in a cross sectional area of the slot is increased. Examples of art related to a stator of a rotary electric machine having the above-mentioned structure are disclosed in the following publications.
Japanese Patent Laid-Open Publication No. 2000-156943 discloses a highly efficient and compact stator of a rotary electric machine, which is applicable to multi-phase alternating winding and concentrated winding. This stator of a rotary electric machine includes tooth cores; a stator winding provided at a portion between adjacent tooth cores on the inner peripheral side, that is, the side on which there is the axis of rotation of the rotary electric machine; and core-back cores each of which is provided at a portion between the adjacent tooth cores on the outer peripheral side, that is, the outer side of the rotary electric machine. In this stator, the tooth core includes a bridge which continuously connects an end portion of the tooth core on the inner peripheral side to an end portion of an adjacent tooth core on the inner peripheral side.
In the stator of a rotary electric machine disclosed in the above publication, the stator core is divided into a tooth core portion and a core-back core portion. After a stator winding is fitted to a slot portion between the tooth core portions, the core-back core portion is pressed into a portion between the tooth core portions in a radial direction. It is therefore possible to provide the stator core which is applicable to multi-phase alternating winding and concentrated winding, and which can increase the proportion of the cross sectional area of the coil in the cross sectional area of the slot, thereby reducing a copper loss.
Other than this structure, there are examples of a structure of a stator core which is divided into two parts. The examples are a structure in which a single coil, that is wound around a bobbin, is fitted to the stator separately from the stator core; a structure in which, in a division motor obtained by dividing the stator core, teeth are coupled to each other while the width of the coupling remains small, the teeth are deployed in the circumferential direction, and windings are fitted to three slot portions of the stator simultaneously using three nozzles, whereby productivity is increased and cost reduction is realized; a structure in which windings are wound around the teeth, that are not coupled to each other, by spindle winding using multiple rotational axes, and the like.
Meanwhile, examples of related art of a stator of a rotary electric machine using a U-shaped coil are disclosed in the following publications.
Japanese Patent Laid-Open Publication No. 2001-292548 discloses a stator of a rotary electric machine, in which the length of a coil end portion is considerably reduced. In this stator of a rotary electric machine, stator coils are fitted to multiple slots of a stator core. In this stator, a straight wire constituting a coil is formed in a U-shape in advance. Then, two straight portions are inserted in slots adjacent to each other through a tooth portion of the stator. Then, a coil constituting a one-turn closed circuit is formed by connecting both ends of the U-shaped coil using a thin plate bar-like piece. By inserting such coils in plurality, a coil having a predetermined number of turns is formed. When the both ends of the U-shaped coil are connected to each other by overlapping the thin plate bar-like piece with the both ends, the thickness of a portion of each end, which overlaps with the thin plate bar-like piece, is reduced by half, and the thickness of a portion of the thin plate bar-like piece, which overlaps with the end, is reduced by half. Thus, the total thickness of the overlapping portion of the end and the overlapping portion of the thin plate bar-like piece corresponds to the thickness of the straight coil, when the end of the coil and the thin plate bar-like piece are overlapped with each other. The thickness of the left end of the coil is reduced by half at the surface toward the internal diameter of the stator. The coil is formed in advance such that the thickness of the right end of the coil is reduced by half at the surface toward the external diameter of the coil. Meanwhile, the thickness of the thin plate bar-like piece is reduced by half at the surface opposite to the surface of the coil at which the thickness of the end of the coil is reduced by half. When the coil and the thin plate bar-like piece are overlapped with each other, the coil and the thin plate bar-like piece are connected to each other such that two straight portions of the U-shaped coil sandwich the thin plate bar-like piece.
In the stator of a rotary electric machine disclosed in Japanese Patent Laid-Open Publication No. 2001-292548, a stride width of the coil is decided based on the width of the adjacent slot. Therefore, the length of a U-shaped portion which protrudes from the stator core in the axial direction corresponds to the width of the adjacent slot. Meanwhile, the portions of the coil, which protrude from the stator core at the side of the end portion of the coil, are connected to each other by the thin plate bar-like piece. Accordingly, only the width corresponding to the width of the thin plate bar-like piece is required in the axial direction. As a result, it is possible to provide the stator in which the length of the coil end portion is reliably reduced.
Japanese Patent Laid-Open Publication No. 2002-153002 discloses a stator of a rotary electric machine in which insulation performance and cooling capability of a coil are increased. This stator of a rotary electric machine includes a stator core; and a stator coil which is fitted to a slot of the stator core so as to be wound around a tooth portion of the stator core. The stator coil is formed by laminating U-shaped coils each of which is formed in a U-shape in advance. The stator coil is inserted into slots adjacent to each other through the tooth portion of the stator. The coil having a predetermined number of turns is obtained by connecting the end portion of the U-shaped coil to the end portion of the adjacent U-shaped coil.
In the stator of a rotary electric machine disclosed in the above publication, even when a coil in which winding tension become excessive, for example, a straight coil or a heavy line coil is used, an insulation member such as a bobbin is prevented from being damaged, a laminated and fastened tooth core is prevented from being deformed, and the coil is prevented from being damaged. As a result, the insulation performance of the coil can be increased. Also, it is not necessary to increase the thickness of the bobbin in order to prevent the bobbin from being damaged. Accordingly, heat conductivity of the bobbin is not reduced. As a result, the cooling ability of a high-temperature coil can be increased.
However, when a coil is directly fitted to a stator of a rotary electric machine by a nozzle, as shown in FIG. 22, a nozzle 300 enters a slot 304 of a stator core 302. The nozzle 300 winds a copper wire around a tooth 308 formed between a slot 304 and a slot 310 so as to form a coil 306. In such a structure, there is a problem that a space for winding is occupied by the nozzle by the size of the nozzle 300, and the proportion of the cross sectional area of the winding in the cross sectional area of the slot cannot be increased. Japanese Patent Laid-Open Publication No. 2001-292548 and Japanese Patent Laid-Open Publication No. 2002-153002 do not disclose a technology for solving this problem.
Also, in the technology disclosed in Japanese Patent Laid-Open Publication No. 2000-156943, the tip portions of the teeth on the inner periphery are coupled to each other in order to reduce the number of divisions of the core. However, there is a problem that the die life is reduced since the width of coupling is small. Also, there is a problem that, since the core, whose inner periphery is divided into multiple portions, leaks the magnetic flux of both the coil and a magnet, the size of the core is increased. Further, there is a problem that an iron loss is increased excessively since ineffective leakage flux circulates in the core whose inner periphery is divided into multiple portions. Namely, an over current is generated due to the leakage flux, and an electric power loss is caused due to the over current. Also, a stress for fixation is applied due to caulking after annealing of the core, which causes a problem that an iron loss is increased.
Meanwhile, when part of the teeth are coupled to each other while the width of coupling remains small, after winding is fitted to the deployed core, the joints are welded, or caulking is performed using another member on the outer periphery, when the teeth are arranged in a circle. At this time, the entire iron loss deteriorates by 30% by creating a high level of distortion in iron (an electromagnetic steel plate).
Also, according to the relationship among heat capacity, amount of generated heat and amount of released heat, the relation being represented by current density, generally, heat is most likely to be generated in the coil end portion when a high load is applied. Therefore, this fact needs to be taken into consideration when the size of the motor is decided.